This invention relates to core end plugs and, more particularly, end plugs for mounting rolls of photosensitive material in graphic art devices such as platemakers.
Photosensitive materials are typically supplied in roll form by winding the photosensitive material onto a core. The core is disposed of once all the photosensitive material has been used. Paperboard is the most common material for the core because of its low cost. The interface between the roll of photosensitive material and most devices, which expose the photosensitive material, is the inside diameter of the paperboard core. On many devices that expose photosensitive material, such as platemakers, the position of the photosensitive material must be accurately controlled to allow the image to be accurately placed on the material. This requires a tight connection between the paperboard core and its mounting within the device. A loose connection would allow movement between the core and its mounting and therefore, poor registration between the image and the material. A tight connection becomes difficult because of manufacturing variations in the paperboard core. The inside diameter of the core can vary by as much as 1.2 mm. To accommodate this variation, the mounting in the device must either be oversized, adjustable in size, or tapered in size. These options present difficulties. An oversized mounting makes it difficult to install and remove because of the force required to press the mounting into the core. An adjustable mounting adds complexity and cost to the device and is prone to user error. A tapered fit changes the axial position of the roll.
This invention provides an interface between a photosensitive material cassette and the paperboard core of the roll mounted therein. According to this invention, a core end plug comprises a cylindrical band of stiffly flexible plastic material having ends defining a longitudinal gap therein. A plurality of radial webs extend inwardly from the band. A pair of the webs are opposite each other and are provided with first and second elongated apertures having parallel longitudinal sides defining identical acute angles of about 3xc2x0 to a first diameter of the band. A third web defines third and fourth elongated apertures having parallel longitudinal sides and having a common major axis aligned with a second diameter of the band which is perpendicular to the first diameter.
A core end plug is easily fitted into each end of a roll core and may be cemented therein to be disposed with the core. Radially extending tabs are provided on the outer edges of each band to butt against the ends of the roll of material.
A mounting plate is inserted into to each core end plug. Each mounting plate has first and second pins equidistantly spaced from a central axis of the plate and are respectively received in the first and second apertures of the opposite pair of webs. A third pin on the mounting plate is received in the third aperture in the third web.
A mounting shaft extends through a central aperture in each mounting plate and through the fourth aperture in the third web. The axis of the shaft remains colinear with the axis of the core for all degrees of flexure of the band to fit into the core. The angled slots or apertures in the first and second webs shift the position of the first and second pins of the mounting plate relative to its end plug as the diameter of the band is varied by flexure so that the axis of the mounting shaft is always coaxial with the axis of the core. This prevents wobble of the roll while the sheet material is being pulled from the roll.